JP4351008B2 - Uninterruptible power system - Google Patents

Description

  The present invention relates to an uninterruptible power supply that supplies stable power to a load even when an input commercial power supply fluctuates, and more particularly to a technique for reducing loss of the uninterruptible power supply.

  FIG. 5 shows a series-parallel compensation type three-phase converter as a conventional circuit example. In the circuit of FIG. 5, the secondary winding of the transformer 1 is connected in series to the AC bus between the AC input terminal 11 and the AC output terminal 12, and the primary winding of the transformer 1 is a second circuit comprising a semiconductor bridge. An AC side terminal of one DC / AC converter 2 (hereinafter referred to as series INV) is connected via a filter 3 that removes harmonic components caused by switching. The AC side terminal of the second DC / AC converter 4 (hereinafter referred to as a parallel INV) composed of a semiconductor bridge having a direct current portion in common with the series INV2 is connected to the AC via a filter 5 that removes harmonic components due to switching. Connected to the output terminal. Further, a storage battery 6 is connected to a common direct current portion of the series INV2 and the parallel INV4.

  In such a circuit configuration, when the power supply voltage of the input commercial power supply 7 connected to the AC input terminal fluctuates, the secondary voltage of the transformer 1 is adjusted by controlling the series INV2, and the fluctuation of the input commercial power supply Is compensated by the secondary voltage of the transformer, and a stable voltage can be supplied to the AC output terminal. At this time, if it is determined that the fluctuation of the input commercial power supply 7 is a voltage drop state with respect to the target voltage, the transformer 1 injects electric power to flow a load current by voltage addition, and energy for the electric power addition. Is supplied from the AC bus by causing the parallel INV4 to perform a converter operation (rectifier operation). On the other hand, if it is determined that the fluctuation of the input commercial power supply 7 is in a voltage rising state, the transformer 1 absorbs power because the load current flows by voltage subtraction, and the absorbed energy causes the parallel INV 4 to operate as an inverter. It is regenerated to the AC bus. The voltage waveform of each part at this time is shown in FIG.

  In addition, when the input commercial power supply fails, the input side ACSW 8 is opened to disconnect the commercial power supply 7 from the AC bus, and the DC power of the storage battery 6 is converted to AC by the parallel INV 4 to supply stable power to the load 9. I can do it. Detailed operation of such an uninterruptible power supply is disclosed in Patent Literature 1, Patent Literature 2, and the like.

  Here, in recent years, in the uninterruptible power supply as described above, improvement in apparatus efficiency has become a major issue. In the conventional circuit shown in FIG. 5, the series INV2 performs an operation of compensating for the difference from the target value when the voltage of the input commercial power supply 7 deviates from the target value. However, when the input voltage is near the target value, the compensation is performed. Minutes are almost zero. However, since an input current flows to the series INV2 via the transformer 1, even if the compensation voltage is zero, a conduction loss and a switching loss are generated in the semiconductor bridge of the series INV2, resulting in a decrease in conversion efficiency.

Considering such a case, it is also considered that a circuit for bypassing the series compensator is separately provided so that voltage compensation by the series INV2 is not performed only in the voltage region where the fluctuation of the input commercial power supply voltage is small. (See Patent Document 3).
US Pat. No. 4,651,265 Japanese Patent No. 3390007 JP 2000-184622 A

  However, the provision of a separate bypass circuit as in Patent Document 3 for the purpose of improving the conversion efficiency leads to an increase in the size of the circuit device as a whole, which in turn increases the cost.

In view of such problems, in the present invention, a series compensation transformer secondary winding connected to an AC bus between an input commercial power supply and an AC output, and an AC output is connected to the primary winding of the series compensation transformer. A first DC / AC converter, a second DC / AC converter having a direct current section common to the first DC / AC converter and an AC output connected to the AC bus, and the series compensation transformer. An uninterruptible power supply comprising an AC switch for short-circuiting the primary side of
When the voltage of the input commercial power supply is outside a predetermined range, the voltage generated in the series compensation transformer by the first DC / AC converter is adjusted,
When the voltage of the input commercial power source is within a predetermined range, the AC switch is ignited to short-circuit the primary side of the series compensation transformer.

  According to the present invention, when the input commercial power supply voltage is in a predetermined range, the series compensation transformer can be made non-voltage and the converter can be stopped during that time, so that the converter flow loss is reduced. In addition, because the transformer short-circuit AC switch installed on the primary side of the transformer is used for protection in the event of converter failure, it not only increases the conversion efficiency but also has a function for protection in the event of converter failure. And increase in the size and cost of the apparatus can be avoided.

  In the present invention, the converter protection switch provided on the series INV side of the compensation transformer is used and turned on in a region where the input commercial power supply voltage does not vary so much that the series INV is stopped to improve the converter efficiency. .

  FIG. 1 shows an implementation circuit of the present invention. In this embodiment, the primary winding of the series compensation transformer 1 is provided with a short-circuit AC switch (short-circuit ACSW 10). Here, the short-circuit AC switch is used for protection when the converter fails. Use the existing one provided as. Here, the technical significance of providing an AC switch for protecting the converter on the primary side of the transformer will be described first.

For example, when a series INV or parallel INV fails, the secondary side of the transformer 1 is short-circuited to make no voltage, and it is necessary to avoid applying a high voltage to the transformer primary side by the failed converter. At this time, a high voltage is generated on the primary side of the transformer 1, while the current flowing on the primary side of the transformer becomes smaller than the secondary current by a turn ratio. For this reason, it is preferable that the short-circuit AC switch is provided on the primary side which has a small current resistance. Normally, the compensation voltage due to the series INV is approximately + 15% to −15%, and therefore the winding ratio is larger on the primary side, such as the secondary side 15 with respect to the primary side 100, so that the current flowing in the primary side Is smaller than the secondary side by the turn ratio.

  Next, FIG. 2 shows the operation of the shorting AC switch (ACSW10) and the operation of the series INV2 with respect to the voltage state of the input commercial power supply 7. If the voltage of the input commercial power supply 7 is equal to or lower than the target voltage value −n1 (V), the short-circuit ACSW 10 is turned OFF (opened), and the series INV2 is controlled to generate a voltage that is insufficient with respect to the target voltage on the transformer secondary side. To do. If the voltage of the input commercial power supply 7 is equal to or higher than the target voltage value + n2 (V), the short-circuit ACSW 10 is turned off (opened), and the series INV2 is controlled so as to reduce an excessive voltage with respect to the target voltage on the transformer secondary side. To do. On the other hand, when the input commercial power supply voltage is in the range of the target voltage value −1n (V) to the target voltage value + n2 (V), the short-circuit ACSW 10 is turned ON (short circuit) and the series INV2 is stopped (gate OFF). Thus, the voltage generated on the secondary side of the transformer is made zero. Here, the value of n1 or n2 is appropriately set according to the required output voltage fluctuation range.

  By performing the above operation, the output voltage becomes the target value when the voltage of the input commercial power supply 7 deviates from a predetermined range, as shown by the solid line in FIG. When it is within the range, output voltage = input commercial power supply voltage (no compensation). Since the series INV is stopped in the non-compensation range, there is no loss of the semiconductor bridge circuit, and the generated loss is only the copper loss due to the short circuit of the transformer primary winding and the conduction loss of the short-circuit AC switch.

  FIG. 3 is a circuit diagram showing the embodiment of FIG. 1 as an example of a three-phase converter. A short-circuit AC switch (ACSW10) is provided in each winding wound for each phase on the primary side of the transformer. The operation is the same as in FIG.

  FIG. 4 is a diagram showing an embodiment in which a parallel INV 4 is connected to the input commercial power supply side of the series compensation transformer 1. The embodiment shown in FIG. 1 is the same as the embodiment shown in FIG. 1 except that the connection relationship between the series INV and the parallel INV is reversed with respect to the direction from the input commercial power source to the load. This is also the same as the embodiment shown in FIG.

It is the figure which showed 1st Embodiment. It is a compensation operation | movement waveform diagram of 1st Embodiment. It is the figure which showed 2nd Embodiment. It is the figure which showed 3rd Embodiment. It is the figure which showed the conventional embodiment. It is an operation waveform diagram of each part of the conventional embodiment.

Explanation of symbols

1 Series compensation transformer 2 Series INV
3 High frequency rejection filter 4 Parallel INV
5 High frequency rejection filter 6 Storage battery 7 AC input power supply 8 Input SW
9 Load 10 Short-circuit ACSW
11 AC input terminal 12 AC output terminal

Claims (1)

A series compensation transformer secondary winding connected to the AC bus between the input commercial power supply and the AC output; a first DC / AC converter having an AC output connected to the primary winding of the series compensation transformer; An AC switch for short-circuiting a primary side of the series compensation transformer, and a second DC / AC converter having a DC unit in common with the first DC / AC converter and having an AC output connected to the AC bus. In an uninterruptible power supply comprising:
When the voltage of the input commercial power supply is outside a predetermined range, the voltage generated in the series compensation transformer by the first DC / AC converter is adjusted,
When the voltage of the said input commercial power supply is in a predetermined range, the AC switch is ignited and the primary side of the series compensation transformer is short-circuited.

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